Humans have only one sense, not five

Humans do not have five senses but most likely one, according to a neuroscientist in the US who suggests that taste, smell, touch, sound and sight may be part of the same system.

Don Katz, an associate professor of psychology at Brandeis University in the US, has been investigating the interconnection of smell and taste in rats. In 2009, he showed that when rats lose their ability to taste, it alters their sense of smell. Two years later, he published a paper suggesting that rats depend on smell as much as taste to determine what food they like.

In a new study published in the journal Current Biology, Katz showed what happened when a rat’s sense of taste is shut down. Using an optical probe, he turned off the brain cells in the animal’s primary olfactory cortex that process taste signals from the mouth.

There was an immediate impact on the firing patterns of the neurons handling smell. In fact, the smell neurons were transformed so radically the rat could no longer recognise familiar odours.

These findings about the interdependence of taste and smell have led Katz to speculate that they are one single sense. He dubbed it the “chemosensory system”.

“How things taste depends on a lot of other factors than what’s on the tongue. We think that taste and smell are part of one large system with two doors, the mouth and the nose,” Katz said.

Other researchers have shown that sound, touch, and sight are also inextricably connected. This leads Katz to believe that all our senses belong to a single system.

Katz likened the brain to a computer fed an immense amount of data so it can generate a single, simplified finding. For the programme to run, information must be gathered through all the senses. But we don’t realise this. We are only aware of programme’s final result, which is the illusion that only one sense is responsible for what we experience, according to Katz.